The present invention relates to a control apparatus for precisely controlling, for example, hardening depth and hardness of a hardened surface of carbon steel by a laser beam or an electron beam.
FIG. 9 is a perspective view showing a conventional laser hardening apparatus disclosed, for example, in Japanese Patent Publication No. 12726/1984 official gazette. In FIG. 9, reference numeral 1 designates a laser beam oscillated from a laser oscillator, numeral 2 designates a hardened material such as carbon steel, and numeral 3 designates a hardened portion formed on the surface of the hardened material 2. Reference numeral 4 designates a moving direction of the hardened material 2, which moves at a speed V.
The conventional laser hardening apparatus is constructed as described above, and the laser beam 1, and the material 2 to be hardened moves in a direction of an arrow 4 at the speed V while the hardened material 2 is being emitted by the laser beam 1. A temperature hysteresis at an arbitrary position of the hardened material 2 in this process is shown in FIG. 10. In FIG. 10, an abscissa axis indicates time, an ordinate axis indicates temperature, and symbols Ms, Ac.sub.3 and Tmp denote martensite transformation temperature, austenite transformation temperature and melting temperature, respectively. When the beam is emitted, the material is heated from a time 0 to a time t.sub.1, maintained at the temperature equal to and higher than the austenite transformation temperature Ac.sub.3 from the time t.sub.1 to a time t.sub.2, the beam emission is then completed, and the material is cooled after the time t.sub.2. The cooling velocity of the material 2 to be hardened in this cooling step is sufficient to cause the martensite transformation to occur in the material with the result that the laser emitted portion is hardened. An example of hardness distribution in the section of the hardened portion of the material 2 is shown in FIG. 11.
In the above-described conventional laser hardening method, hardening conditions such as the output of the laser beam and the hardening velocity of the material 2 to be hardened have been set in advance before hardening, and the hardening conditions has not been altered during the hardening step. When the pretreating conditions of the material 2 to be hardened and the output of the laser beam are varied, a drawback arises that the temperature hysteresis shown in FIG. 10 is similarly altered so that the hardening depth and hardness of the material to be hardened cannot be obtained as set.